1. Field of the Invention
This invention is in the field of methods and apparatus for cleaning the top surfaces of raised I/O terminals of semiconductor elements of a semiconductor wafer by relative movement between the top surfaces of the I/O terminals and a planar surface of mild abrasive pressed against such surfaces.
2. Description of the Prior Art
Some integrated circuits (IC) chips are provided with I/O terminals or bumps. These I/O terminals or I/O bumps are made out of gold, for example, and project a substantial distance above the passivation layer of such chips; on the order of from 15 to 26 microns. Chips with I/O bumps are produced by conventional manufacturing techniques starting with a wafer cut from a single crystal of essentially pure silicon. A large number of large scale IC chips can be obtained from one such wafer. The portions of the wafer which become an IC chip while still an integral part of a wafer is referred to in this application as elements. The semiconductor elements after being severed by sawing are thereafter called chips. The I/O bumps of each element, or chip, are formed on the IC elements while they are still integral with the wafer.
To facilitate automating the process of reflow bonding leads to the I/O bumps of chips, a step in the process of manufacturing electronic devices, it is desirable that the outer surfaces of all the bumps of an element, and in fact all the bumps of all the elements of a wafer lie in the same plane, the I/O plane, which I/O plane is spaced above the upper surface of the wafer and is substantially parallel to the upper surface of the wafer, and thus to the upper surfaces of the elements of the wafer. The I/O bumps are most commonly made of a noble metal such as gold because of the resistance of such metals to corrosion, and because such metals are reliably reflow bondable to electronic leads. However, in reflow bonding I/O bumps of such chips to electronic leads, the strength of the reflow bonds, or joints, varies widely with many being unacceptably weak while others are satisfactorily strong. Such variations occur even between I/O terminals of one chip as well as between the I/O terminals, or bumps, of chips from the same wafer. The exact cause of the variation in bond strength between an I/O bump and electronic lead bonded to the bump is not known. It is believed that notwithstanding the characteristics of gold, for example, that the top surfaces of the I/O bumps are adversely affected by the process steps that occur between the time the I/O bumps are formed and the IC chips are bonded to a lead frame with the result that the strength of the bonds vary widely. Tests have revealed traces of some metals on the surface of the I/O bumps such as titanium, which is used in some of the process steps, and it is also believed that organic materials may be adversely affecting the exposed surfaces of the I/O bumps. At this time, however, the exact cause of vibration in strength of solder bonds is not known.